The present invention relates to apparatus for treating a gas stream. The invention finds particular application in the treatment of a gas stream exhaust from a process chamber used in, for example, the semiconductor, solar or flat panel display industry.
One step in the fabrication of semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of vapour precursors. One known technique for depositing a thin film on a substrate is chemical vapour deposition (CVD), which is commonly plasma enhanced. In this technique, process gases are supplied to a process chamber, housing the substrate, in which they react to form a thin film over the surface of the substrate. Examples of gases supplied to the process chamber to form a thin film include, but are not restricted to: Silane and ammonia for the formation of a silicon nitride film; Silane, ammonia and nitrous oxide for the formation of a SiON film; TEOS and one of oxygen and ozone for the formation of a silicon oxide film; and Al(CH3)3 and water vapour for the formation of an aluminium oxide film.
Gases exhausted from a process chamber can be treated with high efficiency and at a relatively low cost using a plasma abatement device. In the plasma abatement process, the gas stream to be treated is conveyed to a thermal atmospheric pressure plasma discharge (a plasma flare) which is primarily a source of heat. The plasma is preferably formed from an inert gas such as nitrogen and the process gasses passed to the flare subsequent to its formation as this protects the plasma forming device from damage. The plasma causes dissociation of the gas stream into reactive species, such as radicals, which can combine with oxygen or hydrogen species (also conveyed to the plasma flare) to produce relatively stable by-products.
A reaction chamber is located downstream of the plasma generator. The purpose of the reaction chamber is to provide a reaction space, remote from the plasma forming device, in which the gases exhausted from the process chamber can be treated by the plasma and react with additional reagent gases such as oxygen or hydrogen. The reaction chamber may consist of a pipe of dimensions which may for example be approximately 30 mm to 50 mm in diameter and 90 mm to 150 mm in length.
The noxious gases produced in the process chamber, namely unused precursor gases and the reaction by-products, must be treated as and when they are exhausted from the process chamber. They are not stored and then treated. Accordingly the plasma abatement device, sometimes referred to as a plasma burner, or torch, must be operational during processing. If for whatever reason the burner stops working or it needs to be taken off line for cleaning or repair the substrate processing also has to stop. This is clearly not desirable since the processing ideally runs continuously 24 hours and day, seven days a week. Accordingly it has been known to have a back up plasma burner device which can be brought in online should the main plasma burner break down or be taken off-line for any reason. However this is a very expensive solution to the problem since a very expensive plasma burner is kept largely inoperative a lot of the time.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.